I think everyone here would agree with this statement to some extent.
Any area of the industry can be the most profitable.
By this I mean that if my machines are setup to run 8-10 gallons per minute then with a little experience I should be able to make good margins with flatwork. If my rig is setup with 4 fatboys, and a 500 gallon soap tank, then I should be capable of knocking out several $4-500 roofs per day. It all depends upon which area you really want to conquer. As i say to potential customers that give me the excuse "I have a hood cleaner do my concrete" you can be good at all facits of the busines however to really make alot of money and be great at it you will need to narrow it down to a couple of areas like Large Buildings and flatwork or flatwork and hoods, or hoods and fire systems, ..... If i remember correctly Ron made a statement a while back that was something along these lines as well, he used to do maintenance for properties, lawnscaping, and probably anything else you can think of